But it appears even more mysterious as to what she was doing where she was found at that time of night if she'd intended to travel to Tunbridge Wells. Surely she wouldn't have travelled at that hour (if a train was even available at that hour) and kept her aunt up until the wee small hours? And why all that money and jewellery?
I'm not seeing this as a street robbery. Surely she had to have known Top Hat man?

It's easy to understand why Mr Nelson said that the he believed that the two men intended to rob his daughter. He wasn't there so he couldn't possibly know. It's likeliest that he wanted to distract people from thinking/asking what a 'respectable' woman was doing out alone at that time of night.